Carbon materials are applied for low temperature fuel cells, electrodes of supercapacitors and lithium-ion secondary batteries or catalyst carriers in liquid-phase catalytic reaction. Therefore, the carbon material becomes important more than ever while the cost reduction for the production of the carbon materials is more and more required. In the use of the carbon materials as the electrodes or the catalyst carriers, the high porosities of the respective carbon materials are important in view of high fluidity of gas and liquid. In the use of the carbon materials as the electrodes, the high electric conductivities and current densities of the respective carbon materials are important.
As negative electrodes of lithium-ion secondary batteries which may realize respective large capacities are to be employed nanoparticles or nanotubes made of tin, silicon or the like. However, the volume expansion of metal becomes extreme large when the metal absorbs lithium so that the metal is normally broken apart and thus loses the contact to the corresponding electrode immediately, thereby lowering the electric capacity of the lithium-ion secondary battery extremely. This problem renders difficult the practical use of the lithium-ion secondary battery.
Here, silicon strictly belongs to semiconductor, but is treated as metal in this application because the silicon can exhibit half-metallic properties.
In non-patent document No. 1, in this point of view, silicon-carbon complex materials which are deposited on and bonded to the surfaces of carbon particles, each carbon particle being obtained through high temperature resolution of propylene gas, exhibit high capacity retention of 1270 mAh/cm3 at 20 hour-discharging rate (C/20) and high charge/discharge efficiency of 98% or more even though the silicon-carbon complex materials are fixed to the surfaces of the carbon particles. In high current density region, however, the silicon-carbon complex materials have problems of capacity retention being remarkably reduced and the aforementioned properties such as high capacity retention and high charge/discharge efficiency being not able to be exhibited stably due to the not sufficient specific surface area thereof and the large dependency to the specific surface area from the inner spaces of the voids formed therein.
It is reported, on the other hand, silicon crystal is heated to be vaporized and deposited in a thickness of several μm order on a concave-convex copper film in vacuum atmosphere under the state of silicon microcrystal to form the corresponding negative electrode material (non-patent document No. 2). In this case, the reduction of the charge/discharge characteristic cannot be avoided and the production cost of the negative electrode material is extremely increased (non-patent document No. 3).
In non-patent document No. 1, moreover, active material such as tin, calcium, strontium, barium, iridium or the like, which can form lithium alloy with lithium, is supported in the micropores of activated carbon to form the negative electrode of a lithium-ion secondary battery. However, the upper limited value of additive amount of the active material is only 30% relative to the carbon weight of carbon constituting the activated carbon so that the lithium-ion secondary battery using such a negative electrode cannot have sufficient charge/discharge efficiency.
Patent document No. 1: Patent Number JP4069465
Non patent document No. 1: High-performance lithium-ion anodes using a hierarchical bottom-up approach, A. Magasinski, P. Dixon, B. Hertzberg, A. Kvit, J. Ayala, and G. Yushin, Nature Materials, 9(2010)353-358
Non patent document No. 2: Thick vacuum deposited silicon films suitable for the anode of Li-ion battery, Mikiko Ueda, Junji Suzuki, Kohki Tamura, Kyoichi Sekine, Tsutomu Takamura, Journal of Power Sources, 146(2005)441-444
Non patent docment No. 3: Nano- and bulk-silicon-based insertion anodes for lithium-ion secondary cells, Uday Kasavajjula, Chunsheng Wang, and A. John Appleby, Journal of Power Sources, 163(2007)1003-1039